It is known in this field, to manipulate magnetic domains and optically sense these domains (see, for example, the outline article "Magnetic Bubbles--an Emerging New Memory Technology", A. H. Bobeck et al, Proceedings of the IEEE, Vol. 63, No. 8, August 1975, and "Domain Behavior in Some Transparent Magnetic Oxides", R. C. Sherwood et al, Journal of Applied Physics, Vol. 30, No. 2, February 1959). Further, it is known to measure magnetic fields by means of optical fibers (see, for example, T. Brogaardh et al's U.S. patent application Ser. No. 152,724 filed on May 23rd, 1980 and assigned with the present application to a common assignee). However, none of the techniques mentioned above is capable of measuring small magnetic field strengths with high accuracy by means of optical fibers.
A primary object of the present invention is to provide a fiber-optical measuring apparatus of the kind referred to, by means of which very samll changes in a magnetic domain picture can be sensed with high reproducibility by means of the optical fiber.